The present invention relates to vibration inducing mechanisms, especially for use in ground compaction rollers.
Vibratory rollers typically employ a vibratory mechanism for imparting vibratory characteristics to a large compacting drum. Generally, the vibratory mechanism comprises a rotary shaft on which is mounted one or more eccentric masses which produce the vibratory forces when the shaft is rotated. Since different intensities of vibration are required for different compacting operations, it is desirable that the eccentric mass(es) be adjustable to enable the amplitude of the vibration to be varied.
One manner of adjusting the amplitude of vibration involves varying the relative angular position of a pair of eccentric masses about a drive shaft. That is, by positioning the centers of gravity of the masses closely together, the overall eccentric forces are maximized, and by angularly separating the centers of gravity, the overall eccentric forces tend to be counterbalanced to a greater degree.
Exemplary of such manner of adjustment are the disclosures in U.S. Pat. No. 3,192,839 issued to Vivier on July 6, 1965; U.S. Pat. No. 3,892,496 issued to Martinez on July 1, 1975; U.S. Pat. No. 3,722,381 issued to Tuneblom on Mar. 27, 1973; U.S. Pat. No. 3,670,631 issued to Gaylord on June 20, 1972; and U.S. Pat. No. 3,909,147 issued to Takata on Sept. 30, 1975. Each of those patents discloses a pair of eccentric weights whose relative angular relationship can be adjusted to vary the amplitude of vibration. In the apparatus disclosed in the Tuneblom and Martinez patents, two positions of adjustment of the masses are provided, it being required that the direction of rotation of the drive shaft be reversed to effect adjustment. Also in the Martinez patent an impact dampener is provided to minimize shock when the masses contact. In the apparatus disclosed in the Gaylord patent, separate hydraulic motors are required to separately drive two masses. In Takata the axial displacement of a control rod unlocks one or more movable masses for centrifugally-induced movement to different positions of adjustment; to achieve more than two positions of adjustment, at least two movable masses are required. In the apparatus disclosed in the Vivier patent a drive train is provided for rotating two weights in opposite directions. The drive train includes an axially movable sleeve having helical slots which receive pins projecting from a pinion. By axially moving the sleeve, the slots produce rotation of the pinion in order to vary the angular relationship between the weights.
It will be appreciated that a vibration system which requires that the direction of rotation of the drive shaft be reversed in order to vary the amplitude of vibration, reduces the versatility of the apparatus. For example, in connection with compacting rollers, there are certain rolling operations wherein it is preferable to rotate the eccentric masses in the same direction as the roller, while during other operations it is preferable to rotate the masses in an opposite direction relative to that of the roller. Thus, it would be desirable that adjustment between different amplitudes of vibration be possible in either direction of rotation of the vibrator drive shaft.
Vibrator systems which permit only two positions of adjustment, regardless of the direction of rotation, may not provide a sufficient number of potential amplitudes of vibration to satisfy the usual requirements. Also, vibrators which require separate motors for the weights or a drive train including a helically grooved shaft and pin-carrying pinions may be more complex than is desired.
It is therefore, an object of the present invention to provide a novel vibratory roller which avoids or minimizes shortcomings of the above-described sort.
It is another object of the invention to provide a vibratory roller which enables at least several positions of adjustment to be selected.
It is a further object of the invention to provide for more than two positions of adjustment, in either direction of rotation of the vibrator shaft.
It is an additional object of the invention to provide a vibratory roller which is relatively simple in construction and more easily maintained.
It is still another object of the invention to dampen the impact occurring between a variable mass and a drive shaft.